San Dimas Time is used when a writer wants to add some against-the-clock tension to a Time Travel story without thinking too hard about how little sense that makes. As a result, events in two different time periods are shown to happen concurrently, so that people two years in the past only have X minutes to stop the villain from committing some terrible act in the present, even though they should technically have X minutes plus two years to sort it all out. Or perhaps the heroes have only Y minutes to get to their time machine and prevent the villain from doing something thirty years ago, which obviously makes no sense either. (Whatever "our" next year may bring, there is little risk of its world suddenly having experienced a Nazi victory in 1945.)